Such a respirator has a fresh gas mixer, which provides the breathing gas mixture, a control unit and a rebreathing system. The rebreathing system has a respiration drive, e.g., a fan or a radial compressor, a volume flow sensor located in the inspiratory branch, a CO2 absorber located in the expiratory branch, whose output, combined with that of the fresh gas mixture, is fed again into the inspiratory branch, where a breathing gas escape valve for drawing off excess breathing gas when a pressure limit is reached, and a breathing gas reservoir are connected, mostly in the expiratory branch. The control unit controls the fresh gas mixer and the respiration drive and receives signals from sensors, e.g., from the inspiratory volume flow sensor.
When the expired gas is again returned into the inspiratory branch in such a system, the CO2 must be removed from the expired breathing gas, which is done by means of a CO2 absorber. Breathing lime is typically used as the absorber material in such a CO2 absorber. The gas expired by the patient flows through the breathing lime present in the CO2 absorber. The CO2 present in the breathing gas is now absorbed by the breathing lime and is thus removed from the gas flow. The breathing lime is depleted after a total quantity of CO2 absorbed, which depends on the quantity of breathing lime, and no more CO2 can be absorbed any longer. The expired CO2 would again be introduced into the patient during inspiration, after which correct breathing would not be guaranteed any longer.
The consumption of breathing lime can be recognized from the change in color of the breathing lime, which is associated with the depletion of the breathing lime. However, since it is undesirable, as a rule, to have to replace the breathing lime in the CO2 absorber or the entire CO2 absorber during an operation, it would be very useful if the staff could be provided with information on the state of consumption of the CO2 absorber.
A reliable and accurate calculation of the quantity of CO2 absorber absorbed by the CO2 absorber is not performed in the respirators currently available commercially. Thus, measurement/monitoring of the degree of depletion of the CO2 absorber is not yet possible in practice. An anesthesiologist can therefore use only the change in color of the breathing lime as an indicator for the necessary replacement of the breathing lime. Therefore, it often happens that there is a response only when the CO2 content measured by a connected monitoring unit in the inspiratory air of the patient to be respirated is above preset limit values and corresponding alarms, derived herefrom, warn the operating staff.